With four days to go: the latest opinion polls show a dramatic slump in Newt Gingrich's popularity among Iowa's Republican voters as the avalanche of ads attacking the former Speaker of the House's track record dominate the state's airwaves.

The latest poll shows Gingrich falling to fifth place – and confirms Mitt Romney as the front runner, just ahead of Ron Paul's outsider campaign.

Elsewhere, the campaign of Michele Bachmann struggles with falling ratings, no money and few resources, having been surpassed by Rick Santorum among social conservatives.

And in a sign that some Republicans are still not happy with the current field: a group of "rogue voters" are funding radio ads calling for Iowans to caucus for Sarah Palin.

The candidates themselves continue their high octane campaigning across Iowa, with today in some respects the last full day of campaigning available, with the New Year looming and Monday a federal holiday, before the caucuses themselves take place on Tuesday evening.

Follow all the action here live – and please leave your comments below.

10am: Where in Iowa are the candidates today? Everywhere, that's where.

• Mitt Romney: kicked off the day with a rally starring New Jersey governor Chris Christie at the Hy-Vee Westlakes Shore, in West Des Moines, before jetting off to host a spaghetti dinner in Merrimack, New Hampshire, this evening.

• Ron Paul: holds three town halls later today, in LeMars, the Sioux Center Public Library and the River's Bend Convention Center in Sioux City.

• Rick Santorum: today is watching football day for the Santorum campaign, with a "Pinstripe Bowl watch party" at Buffalo Wild Wings in Ames, and an "Insight Bowl watch party" at the Okoboji Grille in Johnston. Probably some heavy drinking involved. Lock up your daughters, Johnston, Iowa!

• Newt Gingrich: spending the day hanging around coffee bars, apart from calling in to "Maxwell and Pam in the Morning" on Radio KIOA in Des Moines.

• Michele Bachmann: having finished her "Total Loser" bus tour she is back to badgering unsuspecting diners throughout the state. But today's agenda includes a visit to Central Perk, the place where Ross and Rachel hung out on Friends. No, it's not the same one. This one is in Fort Dodge, Iowa.

• Jon Huntsman: a busy day totally ignoring Iowa by hanging out with New Hampshire, a strategy borrowed from teenager dating techniques. Huntsman will repeat his remarks that "Iowa is sooo stupid" while rolling his eyes and making gagging noises.

Heavyweight support for Mitt Romney (right) from New Jersey governor Chris Christie in Iowa this morning. Photograph: Jewel Samad/AFP/Getty Images

A survey finds that 45% of all political ads in Iowa have been attack spots aimed against Gingrich. Only 6% were supportive of the former House speaker. Surprise: Gingrich's approval ratings have sunk like a lead turkey.

You may recall that The Music Man is a story about a good looking, smooth talking phony who comes to town and swindles the locals. Whoever thought it would be a good idea for Mitt Romney to hold an event here — he entered from the far end of the fake Main Street and gripped and grinned his way through a throng of perhaps 400 people — either has a dark sense of humor or no sense of irony.

Bad news for Gingrich and Bachmann, better news for Santorum and surprisingly good news for Rick Perry. Four weeks ago in the same poll, Gingrich got 28%. But if it stays like this then Iowa will have basically delivered a five-way tie.

Also: 27% of the interviews were done on cell phones. As more and more households go cell phone-only, especially in Iowa, that's an important number to watch. And Marist's "likely voter" sample includes Democrats and Independents.

It's about how the Iowa caucuses work and it's written by David Yepsen, who covered the damn things for the Des Moines Register forever – but then if you are a real US politics geek you knew that already.

Speaking in the small town of Nevada, Iowa, at the end of bus tour of the state's 99 counties, she dismissed the polls, insisted she could still win and portrayed herself as the Iron Lady, who would lead the US out of socialism to prosperity, just as she said Margaret Thatcher had done for Britain.

But she has lost the sense of confidence she displayed when, in what now looks to have been the high point of her campaign, she won the Ames straw poll in Iowa in the summer. The crowds at her campaign stops were sparse, and some of those who turned up said they planned to vote for other candidates or had not made up their minds.

A shadowy group of Iowans – named Sarah Palin's Earthquake Movement, after a gag Palin made about only running if there was a huge earthquake – is running radio ads in the Hawkeye State urging voters to "vote rogue" and write in Palin's name when they caucus on Tuesday.

Under Iowa's rules that's perfectly possible: in many cases candidates either vote by raising hands or writing a name on a blank piece of paper.

Ron Paul and Rick Santorum are surging close to Mitt Romney and Newt Gingrich to create an electoral free-for-all going in to the state's Republican presidential caucuses on Tuesday.

"Any one of those four could win," said pollster Del Ali of Research 2000, who conducted the poll for KCCI-TV of Des Moines. "The biggest surge without question is Santorum. Both Paul and Santorum have momentum.

1pm: Like moths to a flame, Republicans can't seem to avoid getting burned on the hoary old Barack Obama birth certificate question.

This time it's one of Mitt Romney's sons, Matt – yes, Mitt really called his son Matt – who has apparently issued a half-hearted apology for bringing up the subject at a Romney campaign event in New Hampshire.

Responding to a question about whether mega-wealthy Mitt Romney will publish his tax returns, Matt foolishly drew a parallel with Obama's birth certificate, until his brother Tagg gave him a wedgie and said he'd tell Dad:

Matt: You know, I heard someone suggest the other day that as soon as Obama releases his grades and birth certificate and sort of a long list of things then maybe [Romney]'d do it.

She had bipolar disease and depression and she gradually acquired some physical ailments, and that introduced me to the whole issue of quality long- term care ... and that introduced me to the issue of Alzheimers.

My emphasis on brain science comes indirectly from dealing with ... See, I am getting very emotional, but dealing with the real problems of real people in my family. And so it's not a theory, it's in fact, my mother.

Later, C-Span picked up a conversation between Gingrich and his 10-year-old grandson Robert. "I was emotional," said Gingrich as he wiped his eyes with a tissue. "It's OK, it's OK," said Robert.

The Guardian's Ewen MacAskill is in Iowa, and draws a parallel with Hillary Clinton's tears on the eve of the New Hampshire primary in 2008:

Newt Gingrich was recalling his mother singing in a choir, saying Christmas carols made him weepy. But he became emotional again when he went on to speak about how his mother, who died in 2003, suffered in later life from a bipolar disorder and needed care.

No-one ever knew for sure whether Clinton's tear were genuine or a campaign ploy. I thought it was genuine, a response to the pressure she was under, having just lost Iowa. Gingrich was probably genuine too. Clinton would probably have won even without the tears. Gingrich is probably not going to win in Iowa, tears or not.

Among those who turned out to see Romney, Rob Reed, 44, a businessman from Waukee, Iowa, said he had narrowed his choice down to Romney or Perry and wanted the person best placed to get Obama out.

Many Christians in Iowa have said cited Romney's Mormonism as a reason against voting for him but Reed, though a Christian, said that will not stop him. "For me, it is electability first and his business acumen second. The fact that he is a Mormon would not keep me from voting for him."

Reed added: "The fact that he has been married to one woman is more important to me than Newt Gingrich, who is on his third wife."

At a Thanksgiving forum in Des Moines in November, also moderated by [Frank] Luntz, Gingrich was one of several candidates who broke down in tears. That time, the trigger was thinking about a friend's baby who was born with a heart defect. Also shedding tears at that event were Rick Perry, Rick Santorum and Herman Cain; Michele Bachmann and Ron Paul managed not to crack.

"I feel like Dr. Phil!" Luntz joked at that earlier event, and it's clear his manipulative lines of questioning – probing the candidates for the emotional pressure-points of family and faith – were responsible for the orgy of tears.

3.09pm: The Associated Press sees the wheels falling off the Bachmann bus as the Iowa caucuses draw near:

Encountering small crowds and fresh viability questions, Republican Michele Bachmann slogged into the final weekend of Iowa caucus campaigning Friday looking for any spark to her flagging bid.

The closing week hasn't been kind to the one-time GOP contender: She's losing staff. She's faced calls to abandon her bid. And she has no money.

The difficulties were evident in two restaurant stops where reporters outnumbered patrons.

"Our effort wasn't to bring crowds out. We were just dropping in," she said outside a café in Early.

Earlier today on Fox News, Bachmann claimed that "many disaffected Democrats" were telling her they were going to vote for her on Tuesday. Oh I bet – several people on Twitter suggested that can only be because they are "disaffected" over Obama's chances against Romney and would prefer her to be the nominee.

3.28pm: Here's the video of Mitt Romney's son making his idiot birther remark about Barack Obama's birth certificate.

I like the headline Buzzfeed has given this video: "Matt Romney's Gonna Get Grounded".

Politics has become a really nasty, vicious, negative business and I think it's disgusting and I think it's dishonest," Gingrich told ABC News aboard his campaign bus in Iowa.

"And I think the people who are running the ads know they are dishonest and I think a person who will do that to try to get to be president offers you no hope that they will be any good as president.

You might think that coming from Gingrich, that's a bit rich. And you'd be right.

4.05pm: The Obama campaign is quick to profit from Matt Romney's birth certificate bumble today, zinging out an email from Obama 2012 campaign manager Jim Messina to the president's supporters:

This is how the Romney campaign thinks it's going to win the Republican primary: by pandering to the dead-ender fringe of extremists who still question where the President was born. We can't make them rewrite their talking points. But we can drive up the cost of this kind of politics.

In an interesting side note, Mitt Romney hasn't shown anyone his birth certificate, even when asked by the Boston Globe.

Why that's even slightly interesting is that there is some minor mystery about Romney's real name, as the Globe reports:

His first name is "Willard,'' after the hotel magnate J. Willard Marriott, his father's best friend.

His middle name comes from his father's cousin, who played quarterback for the Chicago Bears from 1925 to 1929. That cousin's name was "Milton'' and his nickname was "Mitt'' — a totally understandable preference for a football player or a presidential candidate. But what does the birth certificate belonging to the presidential candidate actually state?

Seriously though, who cares?

4.15pm: The Republicans won't be the only one's caucusing on Tuesday night in Iowa. There is a Democratic caucus too, and the party has been making efforts to get its supporters out and voting.

The Obama reelection effort is being constructed on the philosophy that on-the-ground grunt work is more valuable than over-the-airwaves glitz. Fewer places symbolize that better than Iowa. The president's campaign has eight offices in the state – a number that a spokesman for the Iowa Democratic Party said was almost assuredly more than any of the Republican presidential aspirants have. Campaign officials have data points on the ready if you want additional evidence of organization prowess. In Iowa alone, they have held 1,200 training and planning sessions in addition to house parties and phone banks. There have been 350,000 calls to supporters and 4,000 one-on-one meetings.

Interestingly, the NBC News Marist poll [PDF] published this morning showed some suggestions that the work was paying off. Of the 2,900 Iowa voters surveyed, the poll found that 20% planned to take part in the Republican caucuses, while 15% planned to go to the Democratic ones.

Given the huge difference between the two this year, that's not a bad outcome.

4.30pm: Finally, Jon Huntsman – or rather, a Super Pac that supports Huntsman – is having a go at Mitt Romney in New Hampshire.

This paid TV ad – accusing Romney of being a "chameleon" – will be running in New Hampshire, with the Pac spending $300,000 on running it, reports the Washington Post.

4.41pm: In case you were wondering, the Sunday political talkshow line-ups for this week:

Newsmax, the conservative magazine and Web site, will show a 30-minute special on Mr Gingrich throughout the weekend in all of Iowa's major television markets. The program is hosted by Michael Reagan, son of the former president, and makes the case that Mr Gingrich is the strongest candidate to carry forward Ronald Reagan's legacy.

A cracker by Jeff Haynes of Reuters: Tonya Dempster (left) holds Zach Pederson for photographers before a Ron Paul town hall meeting in Le Mars, Iowa.

5.26pm: The Guardian's Ewen MacAskill catches up with Rick Santorum during an ill-timed appearance in a sports bar this afternoon:

The loudest cheers any Republican candidate has heard yet in Iowa came in the Buffalo Wild Wings Grill. But they were not for Santorum. The candidate visited the Ames sportsbar in the middle of an Iowa State college football game against Rutgers, the Pinstripe Bowl. It was a debatable location for a candidate.

Almost everyone in the bar, other than journalists, appeared more interested in the game than in Santorum. As befits his status as the latest surging candidate, there was a huge scrum of journalists barging around the bar with him. Iowans are too polite to turn nasty.

One journalist asked him if it was a wise move to visit a packed bar in the middle of a football game, given he was "pissing" people off. Santorum naturally insisted it was a good location. Many of his answers were drowned out, with the volume rising whenever Iowa State appeared likely to score.

Rick Perry's campaign has hundreds of "strike force" volunteers. Starting last week, they've been flying and driving in from all over the country and booking hotel rooms — all at their own expense, said Perry's Iowa co-chairman Bob Haus.

A fresh wave arrived Thursday, and more are expected daily, Haus said. The campaign trains them to deliver caucus packets to precinct leaders, call undecided voters and spread their personal testimonials, he said.